Grunehogna Kraton

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Geological map of the Grunehogna craton and its surroundings

The Grunehogna Craton is a small fragment of the archaic crust of the earth in Antarctica , which was separated from the Kaapvaal Craton , which is part of the Kalahari Craton , in southern Africa when Gondwana broke up . The Grunehogna craton represents the only block of crust that originated in western Gondwana. The craton is located in the western Queen Maud Land on the Princess Martha coast between 15 ° west and 3 ° east longitude. The name Grunehogna refers to a group of mountain peaks in Ahlmannryggen on the southern edge of the craton.

geology

The Grunehogna Kraton is largely covered with ice. The ice-free areas include the Annandagstoppane- Nunataks, the Ahlmannryggen and the Borg massif or the Borg massivet . The Annandagstoppane Nunataks are outcrops of the basement and rise roughly in the middle of the Kraton area. The other two are mountains and parts of the Ritscherflya Supergroup, which developed in the eastern zone. Information about the geological structure comes indirectly from geophysical exploration or from nunataks , where rocks are directly exposed .

Basement

Kaapvaal kraton with the Zimbabwe kraton and the Limpopo belt which together form the Kalahari kraton

The basement of the Grunehogna craton only appears on three to four small Annandagstoppane nunataks. They mainly consist of leucocratic granites with pegmatite dykes containing garnet . Their crystallization age was determined by means of uranium-lead dating of zirconia to 3,067 mya . Individual detritic crystallites date to 3,433 mya and are therefore the earliest indications of the paleoarchaic basement in Queen Maud Land.

The age of these granites correlates with the granite iodes and volcanites in the African Swaziland and Witwatersrand as well as the age spectrum of the crystallites with the tectono-magmatic processes in the African Kaapvaal craton . From this it was concluded that both cratons formed a tectonic unit over a period of approx. 2,500 mya. The Gesteinschemismus and the oxygen / hafnium - isotopes determination in zircons have sunk and remelted supracrustal rock out as magma sources of Granite. Using the lutetium- hafnium method (Lu-Hf method), crystals with an age of 3,750 and 3,500 mya and probably also around 3,900 mya were determined. They presumably come from the crustal source of the magma or from the surrounding rock of the granite extrusions .

Ritscherflya Supergroup

Borg massif , geomorphological - glaciological map

The Ritscherflya Supergroup forms an approx. 2 kilometer thick sequence of clasts and volcanic rocks that have not been or only slightly deformed and metamporphically overprinted. They formed between 1,130 and 1,107 mya in a subduction regime on the edge of a volcanic island arc complex and accumulated in shallow marine zones to broad river systems . This period falls into the formation phase of the supercontinent Rodinias , which corresponds to the Grenville orogeny or the African Kibaran orogeny. The oldest detritic zircons date to around 3,445 mya, the ages of which correlate with basement samples from the Grunehogna and Kaapvaal cratons. The island arch complex of the Ritscherflya Supergroup developed in the eastern area of ​​the Namaqua-Natal-Maud-Belt, which extended on the southern edge of the then still unified Kaapvaal-Grunehgona-Kraton.

The Ritscherflya Supergroup's contact with the basement is not open. The lowest lithostratigraphic units form the Ahlmannryggen and the Borg massif groups . They developed from igneous tholeiitic extrusions and are up to 1,200 meters thick. Additional magmatites rose by 1,107 mya in the form of up to 400 meters thick mafic reservoirs and dykes . These occurred simultaneously in the Umkondo region of Zimbabwe and Mozambique in the Kaapvaal Kraton.

The Grunehogna Kraton is separated from the Maud Belt by the Jutul Penck Trench . Presumably this trench already represented an old tectonic weak zone in the earth's crust, which was reactivated by 140 mya during the separation of Proto-Africa from Proto-Antarctica and the opening of the Southern Ocean . During this process, the rock units were vertically offset from one another at numerous faults . Trenches collapsed on the southern and eastern edges of the craton, carrying massive loads of sediment from the interior of Antarctica. Today the Jutul-Penck-Graben is filled with glaciers .

The Maud Belt represents a highly deformed and metamorphic orogenic zone consisting of volcanic rocks and sediments . It forms the geosutur between the Grundhogna Kraton on the one hand and the Crohn Kraton with the Shackleton Range on the other. Its development falls in the period of the Rodinia formation from around 1,200 mya, followed by an overprinting during the formation of Gondwana around 530 mya. It stretches from the western to the eastern Dronning-Maud-Land and includes Heimefrontfjella , Kirwanveggen , Sverdrupfjella , Mühlig-Hofmann Mountains , Wohlthatmassiv , Schirmacher-Oase , Sør Rondane as well as Belgica Mountains and Queen Fabiola Mountains (Yamato Mountains), the collectively referred to as the Yamato-Belgica complex .

Individual evidence

  1. ↑ Data sheet of the Australian Antarctic Data Center , accessed April 5, 2010.
  2. ↑ Alexander V. Golynsky et al .: Geologic Significance of Regional Magnetic Anomalies in Coats Land and Western Dronning Maud Land. In: Journal Polarforschung, Volume 67, Pages 91–99, 2012-09-17. PDF
  3. ^ HR Marschall, CJ Hawkesworth, CD Storey, B. Dhuime, PT Leat, HP Meyer and ST Buckle: The Annandagstoppane Granite, East Antarctica: evidence for Archaean intracrustal recycling in the Kaapvaal – Grunehogna Craton from zircon O and Hf isotopes. In: Journal of Petrology Volume 51, Issue 11, Pages 2277 - 2301, November 2010. doi: 10.1093 / petrology / egq057 , alternatively alternatively
  4. ↑ Horst R. Marschall, Chris J. Hawkesworth and Philip T. Leat: Mesoproterozoic subduction under the eastern edge of the Kalahari-Grunehogna Craton preceding Rodinia assembly: The Ritscherflya detrital zircon record, Ahlmannryggen (Dronning Maud Land, Antarctica). In: PrecambrianResearch, 236 (2013) 31-45. doi: 10.1016 / j.precamres.2013.07.006 , alternatively
  5. ↑ AB Moyes, JR Krynauw and JM Barton: The age of the Ritscherflya supergroup and Borgmassivet intrusion, Dronning Maud Land, Antarctica. In: PrecambrianResearch, 236 (2013) 31-45. doi: 10.1017 / S0954102095000125 , alternatively
  6. ↑ L. Tack, MTD Wingate, B. De Waele, J. Meert and others: The Mesoproterozoic Karagwe-Ankole Belt (formerly the NE Kibara Belt): The result of prolonged extensional intracratonic basin development punctuated by two short-lived far-field compressional events In: Precambrian Research 180 (1): 63-84 • June 2010 DOI: 10.1016 / j.precamres.2010.02.022 , alternatively [1]
  7. ^ BM Eglington: Evolution of the Namaqua-Natal Belt, southern Africa - A geochronological and isotope geochemical review. In: Journal of African Earth Sciences 46 (2006) 93-111. doi: 10.1016 / j.jafrearsci.2006.01.014 , PDF
  8. ↑ Michiel O.de Kock, Richard Ernst, Ulf Söderlund, Fred Jourdan, Axel Hofmann and others: Dykes of the 1.11 Ga Umkondo LIP, Southern Africa: Clues to a complex plumbing system. In: Precambrian Research, Volume 249, August 2014, Pages 129-143. doi: 10.1016 / j.precamres.2014.05.006 , alternatively
  9. ↑ X. Huang and W. Jokat: sedimentation and potential venting on the rifted continental margin of Dronning Maud Land. In: Marine Geophysical Researches, 37 (4), pp. 313-324. doi: 10.1007 / s11001-016-9296-x , alternatively
  10. ↑ Andreas Läufer, Joachim Jacobs, Marlina Elburg, Antonia Ruppel, Ilka Kleinhanns and others: Connecting Geology and Geomorphysics: The geodynamic Evolution of Dronning Maud Land from Rodinia to Gondwana. In: International Congress on Polar Research, 6-11 September 2015, Munich, Germany, German Society for Polar Research eV PDF
  11. ↑ Antarctica - Kalahari reconstruction at 180 Ma– new paleomagnetic data (English; PDF; 75 kB), accessed on March 30, 2010

literature

  • JM Barton, R. Klemd, HL Allsopp, SA Auret, YE Copperwaite: The geology and geochronology of the Annandagstoppane granite, western Dronning Maud Land . In: Contributions Mineralogy Petrology . tape 47 , 1987, pp. 488-496 .
  • M. Halpern: Rubidium-Strontium date of possibly three billion years for a granite rock from Antarctica . In: Science . 169, 1970, pp. 977-978.